This invention relates to the discovery of side reactions contributing to yield loss in the chlorination of acetaldoxime in aqueous solution and the development of an improved process that obviates these side reactions and consequently increases yield. This clorination releases a large heat of reaction, 57.5 kilocalories per mole of oxime, and generates HCl. Yield loss is apparently caused by side reactions such as hydrolysis of acetaldoxime and acetohydroxamyl chloride by the acidic solution. The side reactions are rapidly accelerated at high temperatures.
U.S. Pat. No. 3,574,736, issued to J. J. Fuchs, teaches the chlorination of acetaldoxime in aqueous solution using a batch process in which all of the oxime is charged first to a reactor and then chlorine is gradually added. Batch chlorination yields are 10-15% lower than those of continuous chlorination most likely because of hydrolysis of acetaldoxime in acid medium. In addition, the control of temperature rise from the very high heat of reaction is somewhat difficult in a batch process. This control is important for at temperatures above 10.degree. C yield loss evidently due to hydrolysis of the product, acetohydroxamyl chloride, can also be significant.
U.S. Pat. No. 3,658,869, issued to Soloway, discloses a process for chlorination of acetaldoxime by either batch or continuous operation. The continuous operation uses a packed column in which the oxime flows downward, countercurrent to chlorine fed up through the column, and a cooling jacket is used to remove heat of reaction. The composition of the reaction medium varies through the column from aqueous oxime to finished product. Oxime concentration would be as high as 7.5% in the upper part of the reactor, and, therefore, the oxime is quite susceptible to acid hydrolysis. This process method is not advantageous for commercial use. To provide sufficient heat transfer for commercial production rates it would be necessary to provide a multiplicity of jacketed packed tubes. Such equipment would be expensive and difficult to operate. If a larger diameter jacketed column were used, heat transfer would be inefficient and part of the reaction mass would be subjected to high temperatures where hydrolysis is rapid.
As recognized by those skilled in the art, excess chlorine will ordinarily result in overchlorination and production of undesired 1,1,1-dichloronitrosoethane and similarly a deficiency of chlorine will result in underchlorination and the unreacted oxime will represent a yield loss. No accurate and reliable method for preventing such chlorination problems is furnished by prior art processes.